Spiral Crystal Growth in the Czochralski Process—Revisited, with New Interpretations

Abstract

Herein, the features of some Czochralski crystals with spiral morphology are investigated in detail to develop a model for their spiral growth. The case of a cylindrically growing crystal with a spontaneous transition to spiral growth is considered. At the onset of spiral growth, the development of a "foot" in the meniscus region is identified. It is shown that the growth of a foot takes place under "flaring growth conditions." Insufficient axial heat transport through the crystal leads to a concave interface which is behind the flaring growth. The constraints of automatic weight control force the flaring crystal to grow as a spiral. The selection of a single foot is assisted by temperature fluctuations in the melt. Some symmetry breakings during spiral growth, for example, a meniscus deformation by rotation and the azimuthal growth in the meniscus, have been described already by the author earlier. Only recently spiral growth has been encountered with Czochralski silicon, grown at high pulling speed. These hypotheses on spiral growth hold for high-melting-point oxides as well as for the lower melting silicon.